Abstract

A substrate with ease for fabrication is proposed for surface enhanced Raman spectroscopy (SERS). A two-dimensional dielectric grating covered by a thin silver film enables the excitation of both localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs). The finite-difference time-domain simulation results show that the coupling between LSPs and SPPs is able to highly improve the Raman enhancement (2 × 109 as obtained by simulation). In addition, the near-field distribution at the top of cubic bumps along the transverse plane presents a highly regular hotspots pattern, which is required for an ideal SERS substrate.

|E| distributions at the top of cubic bumps along XY plane at various resonance conditions, i.e., the incident wavelength of (a) 450 nm corresponding to the high order LSPs, (b) 637 nm corresponding to the SPPs, and (c) 670 nm corresponding to the first-order LSPs. The colorbar scale is set as ln(|E|).

(a) Absorption spectra for various periods from 426 nm to 546 nm with a 24 nm increment; (b) absorption peak positions versus different periods for LSPs (circles) and SPPs (squares), with corresponding maximum local |E| at resonance wavelength of SPPs (triangles). The silver film thickness is 40 nm, the bump height is 100 nm and the environment is water.

Absorption peak positions at various silver film thicknesses for LSPs (circles) and SPPs (squares), with corresponding maximum local |E| at resonance wavelengths of SPPs (triangles). The structural period is fixed at 475 nm, the bump height is 100 nm and the environment is water.

Absorption peak positions at various environment refractive indices for LSPs (circles), SPPs (squares), and corresponding maximum local |E| at resonance wavelengths of SPPs (triangles). The structural period is fixed at 475 nm, the film thickness is 40 nm and the bump height is 100 nm.